Include stdint.h to make this compile.

Submitted by:	Garance A Drosihn <drosih@rpi.edu>

usr.bin/gcore/elfcore.c

@@ -37,6 +37,7 @@ __FBSDID("$FreeBSD$");
 #include <err.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>